A facile approach for the synthesis of niobia/carbon composites having improved hydrothermal stability for aqueous-phase reactions

• Highly dispersed niobia/carbon acid catalysts were prepared by “deposition–precipitation–carbonization (DPC).”
• The catalysts as-synthesized contain crystalline niobia nanoparticles anchored on the carbon support.
• The novel niobia/carbon catalysts demonstrate stable reactivity for butanol dehydration in the liquid phase.
• Pd supported on the niobia/carbon composites shows stable activity with negligible growth in metal crystallite size.
• The improved hydrothermal stability in aqueous-phase reactions is due to the strong interaction between niobia and carbon.

Oxide supports are generally not stable during aqueous-phase reactions due to hydrolytic attack at elevated temperatures. Previous work has shown that niobia (a solid acid) loses surface area due to formation of large faceted crystallites. We show here that niobia/carbon composites are much more stable under these conditions and allow us to retain oxide functionality and acidic properties at elevated temperatures under aqueous conditions. A simple, one-pot synthesis was developed to generate niobia/carbon composites by a deposition–precipitation–carbonization (DPC) method. This method of preparation is simpler than the conventional impregnation route which would require acid treatment of the carbon to generate functional groups that are necessary for the stabilization of the deposited oxide. The catalysts generated by the DPC method contained highly dispersed niobia with nanoparticles having an average size of ca. 8 nm. For comparison, we also tested a commercially available amorphous niobia (HY-340 from CBMM). The niobia/carbon composites showed improved hydrothermal stability and higher reactivity for butanol dehydration compared with the HY-340. Embedding niobia in carbon helps prevent the growth of oxide crystallite size. In the conversion of gamma valerolactone to pentanoic acid, we found that the niobia/carbon composites helped to preserve the Pd dispersion, leading to improved Pd/Nb2O5/carbon bifunctional catalysts. We see these oxide/carbon composites as promising alternatives to carbon supports for aqueous-phase reactions.

Nanocrystalline niobia is embedded in a carbon matrix via deposition–precipitation–carbonization. The niobia shows improved reactivity for liquid-phase reactions and excellent hydrothermal stability.Figure optionsDownload high-quality image (184 K)Download as PowerPoint slide